Common ground bus for Lionel command control

Dale,

Your choice of the term "ground" is going to confuse you.  Instead of  the DC-oriented terms "Power" and "Ground" I prefer the AC-oriented terms "Hot" and "Common".

Why? Those outside rails do not, and must not, connect to earth ground, i.e., to anything connected to the green wire in your house wiring, or to a cold water pipe, or to the screw on an outlet cover.  If they do TMCC and Legacy won't work.

They can be however, and often are, common to each other, that is electrically connected together (but not connected to earth ground).

In fact the point at which they are connected together is a good point to connect the single antenna wire from the command base, although there are a couple other possibilities as well.

Mike

Thank you for posting the question, Dale!  When our club member who is up on Legacy stated the wire from the Legacy base goes to the common rail, I questioned it in my mind.  I didn’t say anything since as you know, I’m an MTH guy too.  I just checked my TMCC base wire.  It is connected to the terminal block feeding the center rails.  The TMCC base is connected to the TIU with the appropriate cable.  I can run my two TMCC engines and One Legacy engine with the DCS remote fine.  It would seem to me we could use the common bus, but I also would like the Legacy folks to let us know.

Mike, thank you for clarifying common versus ground.  Yes, we mean common, and not tied to an earth ground.

What your doing shouldn’t be a problem. The conventional engines won’t see the Legacy signal no matter what loop they are on even if its present. You can run your conventional trains using the ZW’s handles. You just have to make sure the center rail is totally isolated from any loop seeing the 18v.

If you really are using the ZW for all three loops, you are all ready for TMCC or conventional on any loop in any combination. One wire connection is all that's needed - connect the base(Legacy or TMCC) "U" terminal to one "U" post on the ZW, power up the base, and the installation is complete.

@Dale K  just ran across the post. I too am an MTH guy who just installed a TMCC base linked to my MTH app (no remote control).  I have all my outside rails, which form 3 loops, connect to a single common point near my transformers. The loops are electrically isolated but have interconnected track. All I did was connect the control wire from the TMCC base to the outer track loops. As long as I power above 14 volts, it works like a charm.  Instructions say to connect to the outside rails not the center rail. Of course figuring out the engine address ID is a different matter. I was fortunate in that my TMCC engine was still at the factory setting of 1.

To me an odd thing about the system and in particular the power transformer for the base. The base needs to be connected to the ground plug of the 3 prong AC adapter (which comes with the base). Normal 2 prong transformers will not work. Elsewhere on the forum is an explanation on a work around. The base I originally bought did not have the the power transformer - hence an opportunity for a learning experience. Do not run down that rabbit hole. 

Because TMCC and DCS powers the track at 18 volts all the time, there is no problem I have run across using both at the same time. However if you want to run an old conventional engine with transformer control, you will want to run that engine on an electrically isolated track. 7 or 8 volts feeding DCS engines is not going to make them happy. With the ZW having two power feeds you can run variable voltage on one loop and fixed (18volt) on the other. If you end up wanting to change which loops are running variable and which are running fixed, I installed stereo banana plugs and jacks tied to each loop. This allows me to use a single power output for all 3 loops or 3 power outputs for the 3 loops or any other combination of 2 and 1.  The Z4000 uses banana jacks anyway, so not a big deal. I did use 16 gauge stranded speaker wire for the connection instead of what passes for power connectors in the MTH black and red wire sets. Those look like a melt down waiting to happen. 

lastly, as I found out, if you have the TMCC control signal running through the track, TMCC engines will not respond to transformer variable control. You have to pull the plug on the TMCC base, then they work fine. Since its supposed to be a radio signal using the track as an antenna, I do not think you could run a TMCC engine on one loop and another TMCC engine but under variable control on another loop. Of course if the other engine did not have the TMCC board then no issues.   

Hope this helps.  Jeff

To answer your last question directly  If it is possible, can we use a common ground bus for the three loops? That is exactly what I am doing, as long as we understand "common ground" is referring to the electrical connection for the outer rails.  If using multiple transformers, you are supposed to do this anyway to make sure the power supplied by each transformer is "in phase." [To me black is hot and white is common for 120vac systems, of course MTH flips that with red hot and black common. Can't tell you how many times I goofed that up wiring my layout.] 

Thank you for the reply, Jeff.  I ran an experiment this evening with my TMCC and DCS setup.  I thought I had the TMCC base wire connected to the hot wire, center rail, and so it was.  I was able to run a Legacy engine with the TMCC controller or the DCS controller with the engine in TMCC mode.  I looked it up and learned as you said, Jeff, that the base should be connected to the outside rail.  So I moved it and ran the same engine with the TMCC remote and DCS with no trouble.  Since I had read it was to be connected to the outside rail, I left it there.

Having been in on the initial discussion with Dale, the one thing I haven't done is tie the common from the two loops together since they are wired off the two fixed outputs of the TIU.  I guess it may come down to setting up a circuit that has TMCC/Legacy on one loop and conventional on another with the commons tied together and see what happens.  Out come the screwdriver and alligator clip jumpers again!!!

Simple if you use 1 ZW. You connect the 3 loops together with their outer rails to a terminal and run a wire to one of the 4 ZW ground post. Run a wire from your Legacy or TMCC base to a ZW ground post or even to the terminal strip.
Common grounds work well and you can tie all your commons from lighting/ accessories together to a terminal strip. Saves a lot of wiring.

I think the OP’s question was answered but in case anyone else is interested my clubs new layout is going up in the same manner we use 1 common bus with 4 Hot buses for track and 2 hot buses for accessories. We also used 360W PowerMasters to allow for conventional operation and running DCS in passive mode. We’ve been doing this for almost a year now everything has worked as expected so far. For passive mode I used a 22uh choke Mounted on a PCB in the Hot line from the PowerMaster before the bus.

Here’s a video on the layout. It’s a year old now but might help

Ted and Zachariah, and everyone, being in the same new club as the OP; thank you for your comments.
Ted, we are using my ZW, so your input is appreciated.

Zachariah, as we move forward, we will become more sophisticated.  Thank you for the video.  Our Legacy man, already has shared many ideas for future upgrades. 😊

Semi-related...  If you're using a postwar ZW (or any postwar transformer) for powering any newer engines, check out the threads regarding having faster circuit breakers and TVS diodes.  Without these, it's too easy to fry an engine's electronics.

Mallard, excellent point I forgot to mention!  Thank you!!  I had been using circuit breakers and TVS diodes on the outputs.  I had Harry Henning refurbish my ZW last year, and he included fast circuit breakers and TVS internally while he was at it.  He put a label above the terminal posts indicating this.  If we can’t use this ZW, we will make sure we take proper precautions with whatever we use.

...circuit breakers and TVS diodes...

TVS diodes are mandatory, breakers are optional, if not convenient. Transients occur all of the time, not just at derailments.